1. Field of the Invention
The present invention relates to a photographic film cassette. More particularly, the present invention is an improvement of a spool of a film cassette in which rotation of the spool causes a photographic film leader to advance to the outside of a cassette shell.
2. Description of the Related Art
A known photographic film cassette includes a photographic filmstrip (hereinafter referred to as film) positioned so that the film leader does not protrude from the cassette shell prior to loading the cassette in a camera. Such a cassette is easily loaded into a camera. Simple film-advancing mechanisms of the camera are typically used with this type of cassette and include a construction which rotates a spool to unwind the film, thereby causing the leader to move through a film passageway and exit from the cassette.
In the above-mentioned type of film cassette, the roll of film wound on the spool is prevented from loosening, when the spool is rotated, in order to transmit the rotation of the spool to the leader. In a cassette as disclosed in U.S. Pat. Nos. 4,846,418 and 4,887,776, the spool has a pair of spool pieces slidable relative to each other. A first spool piece is provided with a first flange and a cam follower, whereas the second spool piece is provided with a second flange, which is flat, and a cam groove formed to receive the cam follower. When the spool pieces are rotated relative to one another, the cam follower is guided along the cam groove so as to shorten the interval between both flanges by sliding the spool pieces axially relative to one another. The first flange is provided with a circumferential lip which projects from around its peripheral edge so as to engage with a side of the outermost turn of the roll of film in order to prevent the roll from loosening. When sliding the spool pieces, the outermost turn of the roll is clamped between the flat flange and the inside of the lip of the other flange so that the roll of film is rotatable integrally with the spool and is thus prevented from loosening.
It is, however, difficult to form the first spool piece discussed above. Both the first lipped flange and the cam follower are formed on the first spool piece so as to project from the cylindrical surface of its core. When molding such a spool piece integrally, the cam follower defines an undercut. Such a construction causes excessive complication in an injection molding process used to form the spool. Accordingly, the cam follower for the first spool piece is formed beforehand in a separate manner, such as a pin, which is fixed on the core after welding. Thus, the cost of manufacturing the spool, and thus the cassette, is relatively high.